Flexible pipe system

ABSTRACT

A pipe system is disclosed which includes a corrugated pipe for conduction of fluid, the corrugation defining an asymmetrical wave pattern in an axial plane, to establish a periodically recurring sequence of flow zones of gradually increasing cross section, alternating with nozzles.

United States Patent Kauder 1 I Feb. 22, 1972 [54] FLEXIBLE PIPE SYSTEM[72] Inventor:

[7 3] Assignee:

Knut Kauder, Hannover, Germany Kabelund Metallwerke GutehoffnungshutteAktiengesellschaft, Hannover, Germany I22] Filed: Oct. 16, 1969 I21]Appl. No.2 866,843

[52] U.S.Cl ..l38/l21,138/173,138/178, 138/114, 138/122 [51] Int. Cl..Fl6l 11/12 [58] FieldofSearch ..138/121,l22,173, 178,113, 138/114 [56]References Cited UNITED STATES PATENTS 2,740,427 4/1956 Swan ..138/1222,865,403 12/1958 LeVantine ..138/121 3,058,861 10/1962 Rutter 1 38/1 2l FOREIGN PATENTS 0R APPLICATIONS 1,188 1901 Great Britain ..138/l7311,017 1884 Great Britain l 39/ l 73 8,318 1888 Great Britain.....138/173 96,031 8/1963 Denmark ....l38/12l 721,398 6/1942 Germany....l38/l21 468,583 3/1969 Switzerland 1 38/12 1 PrimaryExaminerI-Ierbert F. Ross Attorney-Smyth, Roston & Pavitt ABSTRACT Apipersystem is disclosed which includes a corrugated pipe for conductionof fluid, the corrugation defining an asymmetrical wave pattern in anaxial plane, to establish a periodically recurring sequence of flowzones of gradually increasing cross section, alternating with nozzles.

7 Claims, 1 Drawing Figure FLEXIBLE PIPE SYSTEM The present inventionrelates to flexible pipes and pipe systems. It is known per se to useflexible pipes particularly for the conduction of liquids or gases. Suchpipes are made flexible particularly to facilitate their owntransportation and installation. In particular, pipes are made flexiblein that they are provided with helical or circular, bellowslikecorrugations. However, corrugated pipes inherently provide larger flowlosses (speed loss for the fluid) than pipes with smooth walls. In orderto keep such losses low, the wave amplitudes of the wall as establishedby the corrugation has been selected to be rather small. But, of course,flexibility of a pipe with little corrugation is likewise reduced andthis in turn limits utilization of such pipes particularly whenflexibility is an-important factor.

It is an object of the present invention to provide an economicallyjustifiable, corrugated pipe which, as far as its mechanical propertiesare concerned, meets the requirements to the optimum and which does notexcessively deteriorate fluid-dynamic performance as compared with asmooth pipe, without however attempting to provide identical hydraulicand fluid dynamical conditions.

It is therefore a particular object of the present invention to providea flexible pipe for the conduction of fluid which is flexible to theextent required but which establishes fluiddynamic conditions which areimproved over the corrugated pipe heretofore used. The pipes asparticularly improved by the present invention are corrugated so thatthe wall of the pipewhen traversing an axial plane defines a wavepattern in direction of flow along the pipes axis.

In accordance with the present invention, it is suggested to provide thecorrugations as an asymmetrical wave pattern whereby particularly, andlooking in the direction of the intended flow, the front or leadingflank of a wave is rather flat and has a small angle corresponding to arather gradual widening of the flow path in the vicinity of that wallportion; and the rear flank of that wave is almost or completelyrectangularly arranged to the direction of flow, corresponding to arather abrupt flow path constriction. A pipe having such asymmetricallycorrugated wall still is highly flexible, but on the other hand, thefluid dynamic conditions established therein are actually not muchdifferent from those of an uncorrugated, smooth type pipe.

For a corrugated pipe one can define an equivalent inside diameter to bethat inside diameter of an uncorrugated pipe having the same flow lossesas the corrugated pipe under consideration. Using this terminology, itwas found that the actual inside diameter and the equivalent insidediameter of a pipe corrugated under observation of the rules inaccordance with the present invention are not significantly different.It was thus found that the flexible pipe in accordance with theinvention meets the requirements as far as mechanical properties as wellas flow dynamics is concerned.

The wave valleys or corrugation grooves of such a pipe establishes flowpath constructions recurring on a periodic basis along the direction offlow. These constrictions can be regarded as a sequence of nozzle ororifices particularly for flow of fluid in the range of to 10 Reynoldsnumbers. Numerous tests have established that a pipe with such anasymmetric corrugation and wave pattern establishes minimum of flowlosses, particularly where, looking in the direction of flow, the frontwave flank of a wave of the pattern has inclinations which is ratherflat and in which the rear flank is at right angles or almost at rightangles to the flow axis. This is, of course, particularly true whencompared with heretofore used symmetric wave pattern.

Considering the flow dynamics, the following observations have beenmade. The widening of the flow path in direction of flow is to occur ata rather shallow angle, as the area of flow path widening was defined asone pertaining to a leading wave flank. Thus, rather gradual wideningcorresponding to a small angle to the flow axis is less abrupt than incase of conventional corrugation. lt is for this reason that the flowseparates later, i.e., at a point of the tube-s wall for a larger insidediameter. Accordingly, the stagnation point at the rear flank islikewise displaced radially outwardly, or more inwardly as to thecorrugation pocket so that there is a relative hydraulic diminishing ofthe size of the flow zone which is disturbed by the corrugation. Thus,the disturbed flow zone measured from the point of separation to thestagnation point is considerably smaller in comparison with theregularly formed wave pattern if the flanks of the corrugation pattemwaves are changed in accordance with the invention. The stagnation pointis oriented at right angles to the direction of flow. The shallowerangle of the leading flank of wave causes an enlargement of the regularflow area so that the chamber in which an eddy is formed becomes smallerso that smaller eddies are formed accordingly. Thus, the principal,central or axial flow is less disturbed. Also, the central flow providesless energy for formation and sustenance of these smaller eddies whencompared with a symmetrical corrugation.

In accordance with a further improvement of the invention, wave depthand wavelength of the asymmetric wave pattern correspond to a symmetricwave pattern of the corrugation. Wave depth or amplitude is defined ashalf of the difference between maximum and minimum inside diameter ofthe tube, minus twice the wall thickness of the tube. Wavelength is, forexample, the distance between the two wave crests (corrugation ridges)measured in the direction of flow along the tube s axis. It was found tobe of advantage, if the ratio of wave depth to half of the wavelengthhas value in between 0.4 and 1.3, but preferably has a value of unity.Tests have actually shown that flow losses are at minimum if thedimensions are chosen to satisfy this rule.

A pipe provided with such corrugation is characterized by a particularstable formation of eddies. This in turn is instrumental in establishingminimum flow resistance for the central flow core as established inaccordance with the inside diameter of the pipe. In particular, a pipewith an inner contour in accordance with the invention establisheseddies having very stable toroidal configuration. In accordance withanother feature of the invention, the radius of curvature of thecorrugation valleys establishing the flow path constriction should belarger than the radius of curvature of the wave crests. It was foundthat this way the pipe establishes a series of nozzles rather thanaperture stops or orifices, as nozzles have lower losses than orifices.

In case liquids are to be conducted through the pipes which are eitherhotter or cooler than the environment, it may be of advantage to providethermal insulation around the pipe. This insulation may be established,for example, by glass wool, or minerals such as perlite. Stillalternatively a layer of foamed plastic can be used for thermallyinsulating the pipe against the exterior. In order to protect thethermally insulating layer against mechanical and/or thermal damagesfrom the outside, the insulation layer is preferably surrounded byanother corrugated lining such as another corrugated pipe of largerdiameter. The wave pattern of the corrugation of the outer pipe normallydoes not have to meet any particular flow requirements. The corrugationsof the outer pipe are thus merely provided to avoid deterioration of theflexibility of the entire pipe system. Thus, flexibility of the outerpipe is the principal factor as to its mechanical properties.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

The FIGURE shows a cross-sectional view of an example of the preferredembodiment of the present invention. It should be emphasized, however,that the illustration is schematic in nature and the wave patternillustrated is actually overemphasized as compared with the overalldiameter of the illustrated pipes themselves.

The pipe system shown in the FIGURE includes an outer corrugated pipe 1and an inner pipe 3, the latter pipe being provided for conducting afluid, the former serving as cover and protection. The space betweenpipes 1 and 3 is filled with a thermally insulating layer 2. The arrowin the figure denotes the direction of flow in inner pipe 3.

Looking in the direction of flow, the asymmetric corrugation of pipe 3has the following configuration. The FIGURE illustrates a sectionthrough an axial plane particularly as far as the axis of the fluidconducting pipe 3 is concerned. The section of pipe 3 in this plane is awave pattern the waves thereof having crests 7 and valleys 6. Anindividual wave can be regarded as having a leading flank 4 and atrailing flank 5.

The front or leading flank 4 has a divergent angle a measured in effectin relation to a direction which is parallel to the axis of the pipe.That angle a is now considerably larger than 90. The rear or trailingflank 5 of each wave so considered, however, extends at right angles tothe direction of flow. That angle does not have to be exactly 90 but itshould be at least close to 90. I

As can be seen, the wave pattern is highly asymmetrical; asymmetry to beunderstood in relation to any crest or any valley of a wave in an axialplane. The outer pipe 1 is shown to be provided with a symmetricalcorrugation pattern, and this illustration facilitates evaluation of therelationships. One can see that the leading flank 4 of each such waveextends longer in axial direction then trailing flank 5, so that theleading flank of the asymmetrical wave is relatively longer than aleading flank of a symmetrical wave of the same wavelength. The leadingflank is a flow region where the cross section through the flow pathwidens. Thus, due to the more gradual cross section increase, separationof flow from the wall occurs later when measured from a valley whichdefines a flow path region of maximum construction. In other words,separation of flow occurs at a larger inner pipe diameter than in caseof a symmetrical wave and corrugation pattern. Accordingly, the zone ofdisturbance as measured from the point of separation to the stagnationor ram point, is considerably smaller. If the contour of the flanks ofthe waves are selected as illustrated and differing from the symmetricalwave pattern of the corrugation accordingly.

Adjacent crests 7 there are established chambers in which eddies areformed. As the separation of the regular flow from the wall is closer tothe crests 7, the chambers and eddies therein are smaller than whencompared with the symmetrical wave pattern. Smaller eddies, however,take less energy from the main flow and disturb the main flow less thanlarger eddies so that the smaller eddies produce smaller overall losses.

As can be seen further from the drawing, the respective radius ofcurvature of valleys 6 is considerably larger than the radius ofcurvature of a crest 7. This in turn establishes a sequence of nozzleswhich establish less losses than orifices. As was mentioned brieflyabove, the wave pattern measured in the direction of flow can also bedefined by a wave length T measured, for example, from peak to peak inthe direction of flow. Further, I can be regarded as the amplitude ofthe wave pattern of the depth of the waves. Amplitude t can also bedefined as outer diameter D of the corrugated pipe minus smallest insidediameter {1 minus twice the wall thickness. It was found to be ofparticular advantage if 2r/T=l, or at least within the range from 0.4 tol .3

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be included.

lclaim:

l. A flexible pipe for conduction of fluid and having a corrugated innerwall, the corrugations defining a wave pattern in any axial direction,the corrugations having a contour and the pipe being installed inrelation to direction of fluid flow therein so that the corrugationshave a divergent flat leading flank with a gradual widening of the crosssection of the flow path in direction of fluid flow, followed by atrailin flank defining a rapid flow path constriction, the trailing flanbeing defined by a wall portion of the corrugated wall extending atleast substantially at right angles to the axis of the pipe and facingthe flow, the corrugations of the wall having amplitude and wavelength,the ratio of amplitude to half the wavelength being within the range of0.4 to 1.3

2. Flexible pipe as in claim 1, the corrugations, having amplitude andwave length corresponding to a symmetrical wave pattern.

3. Flexible pipe as in claim 1, the ratio being unity.

4. Flexible pipe as in claim I, the corrugations having curved crestsand valleys, the crest being where the leading flank merges into thetrailing flank, the radius of curvature of the crest being considerablysmaller than the radius curvature of the valley.

5. Flexible pipe as in claim 1, the pipe being clad with thermallyinsulating material.

6. Flexible pipe as in claim 5, the pipe as clad being covered by aprotective lining.

7. Flexible pipe as in claim 6, the lining being another corru gatedpipe.

1. A flexible pipe for conduction of fluid and having a corrugated innerwall, the corrugations defining a wave pattern in any axial direction,the corrugations having a contour and the pipe being installed inrelation to direction of fluid flow therein so that the corrugationshave a divergent flat leading flank with a gradual widening of the crosssection of the flow path in direction of fluid flow, followed by atrailing flank defining a rapid flow path constriction, the trailingflank being defined by a wall portion of the corrugated wall extendingat least substantially at right angles to the axis of the pipe andfacing the flow, the corrugations of the wall having amplitude andwavelength, the ratio of amplitude to half the wavelength being withinthe range of 0.4 to 1.3
 2. Flexible pipe as in claim 1, thecorrugations, having amplitude and wave length corresponding to asymmetrical wave pattern.
 3. Flexible pipe as in claim 1, the ratiobeing unity.
 4. Flexible pipe as in claim 1, the corrugations havingcurved crests and valleys, the crest being where the leading flankmerges into the trailing flank, the radius of curvature of the crestbeing considerably smaller than the radius curvature of the valley. 5.Flexible pipe as in claim 1, the pipe being clad with thermallyinsulating material.
 6. Flexible pipe as in claim 5, the pipe as cladbeing covered by a protective lining.
 7. Flexible pipe as in claim 6,the lining being another corrugated pipe.